Microwave assisted magnetic recording, MAMR, is one of several future technologies that are expected to extend perpendicular magnetic recording beyond 1 terabit per square inch. In this scheme, a field generator is placed in close proximity to the write element to produce a high frequency oscillating field in the media film plane. The frequency range of the oscillating field could be from 5 GHz to 50 GHz. Because of ferromagnetic resonance (FMR), it becomes possible to switch media grains at fields below their normal coercivity i.e. a lower write field may be used, but only in the immediate vicinity of the microwave assisted write element.
The microwave field generator typically is made of a spin torque oscillator (STO), which resembles a current-perpendicular-to-plane (CPP) GMR or TMR structure in that the current flows perpendicular to the film, although the magnetization directions in the stack are different from those of a CPP GMR/TMR sensor. US patent application US2008/0019040A1 (Zhu et al.) provides details of the STO stack structure.
As shown schematically in FIG. 1, the simplest configuration for STO 11 is a tri-layer stack consisting of spin injection layer SIL 12, interlayer IL 13 (non-magnetic metal or insulating barrier), and field generating layer FGL 14. The SIL magnetization is kept perpendicular to the film, either by an external magnetic field or through its intrinsic magnetic anisotropy. When electrons transit the SIL their spins become polarized by the magnetization present in the SIL. The resulting spin polarization is carried into the FGL by electrons that have crossed interlayer 13. Spin torque oscillation then occurs in the FGL, producing the oscillating field.
In order to utilize STO for MAMR recording, the STO needs to be placed as close as possible to where the writing occurs i.e. on the trailing side of the write pole. It is also very important for the oscillating field from the STO to be perfectly aligned with the write field from the main pole (MP) in the cross track direction so as to retain maximum track density.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Patent Application 2009/0059423 (Yamada et al) shows a spin torque oscillator between a main pole and trailing shield, but no details are given as to how it is fabricated.